Originally Posted by luker
I am excited to see the definitive answer. I have a British freewheel from the late 50's (Cross) and it has no indicator of threading at all. I suspect that the indicators were a 60-70s addition, mostly. I have never seen a real Italian threaded freewheel, but the thread difference would be almost instantly noticeable, wouldn't it?
Italian-thread freewheels use 24 TPI and a 35mm = 1.378" diameter, which is virtually the same as the ISO standard of 24 TPI and 1.375" diameter. However, because the threads are cut at a different angle (think of them as sharper "teeth" in profile), swapping back and forth between Italian and ISO will presumably erode the aluminum threads on the hub shell, leading to potential failure on an out-of-saddle climb or sprint (ouch!). In my experience, mismatched freewheel/hub sets put up a bit more resistance than normal during assembly and disassembly.
Yes, French-threaded freewheels are completely incompatible with Italian and ISO, and blessedly rare in the U.S. (I had one on a circa 1980 Carbolite 103 Peugeot, which also had Swiss BB threading.)
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069